Vehicle safety device

ABSTRACT

The disclosed apparatus detects an imminent collision between a vehicle and an object, by orienting respective receiver and transmitter antennas, mounted on the vehicle, so their patterns intersect and form a crash detecting zone just ahead of the vehicle, and by deriving the relative speed between the vehicle and the object in the crash zone from an undulatory signal radiated by the transmitter antenna and the reflected undulatory signal received from the object. A generator, a directional coupler, and a detector all associated with the antennas, derive the relative speed between the vehicle and the object on the basis of homodyne detection of the transmitted undulatory signals and the reflected undulatory signals. The presence of the objects within the crash zone is indicated by receipt of an undulatory signal above a given level. When both relative speed and level exceed their respective threshold values, threshold circuits issue signals. An AND circuit responds to the signals and actuates a safety device such as an air bag for protecting passengers. To prevent erroneous actuation of the safety device when the vehicle and the object are on course passing each other, antennas on the left and right sides of the vehicle receive reflected signals and form respective Doppler frequencies. A divider determines the relative angle between the vehicle and the object by calculating the ratio of these Doppler frequencies. When the ratio exceeds a predetermined value, comparators direct a signal to disable the AND circuit.

United States Patent Sato et al. Dec. 11, 1973 VEHICLE SAFETY DEVICE[75] Inventors: Kazuo Sato; Tomio Hisatsune; ABSTRACT Mimr" Ilawai ofToyota, Japan The disclosed apparatus detects an imminent collision [73]Assigneez Toyow Jidosha Kogyo Kabushiki between vehicle and an object,by orienting respec- Kaisha, Toyotafihiv Aichbken, tive rece1ver andtransmitter antennas, mounted on Japan the vehicle, so their patternsintersect and form a crash detecting zone just ahead of the vehicle, andby Filed! P 15, 1971 deriving the relative speed between the vehicle and[21] APPL No 134,348 the object in the crash zone from an undulatorysignal radiated by the transmitter antenna and the reflected undulatorysignal received from the object. A genera- Foreign Application PriorityData tor, a directional coupler, and a detector all associated Dec. 27,1970 Japan 45/126238 with the antennas, derive the relative speedbetween the vehicle and the object on the basis of homodyne [52] [1.8.CI. 343/7 ED, 340/ l R, 343/5 PD, detection of the transmittedundulatory signals and the 343/112 CA reflected undulatory signals. Thepresence of the ob- [51] Int. Cl. G0ls 9/02 jects within the crash zoneis indicated by receipt of [58] Field of Search 343/7 ED, 5 PD, 112 CA,an undulatory signal above a given level. When both 343/15; 340/ l Rrelative speed and level exceed their respective threshold values,threshold circuits issue signals. An AND [56] References Cited circuitresponds to the signals and actuates a safety UNITED STATES TE S devicesuch as an air bag for protecting passengers. To 3 283 292 11/1966 Kay340 1 R Prevent erroneous actufition Ofthe Safety device 3338316785/1968 Palmer n 3435 PD the vehicle and the ob ect are on course passingeach 3,343,167 9/|967 Rademacher 3435 PD other, antennas on the left andright sides of the vehi- 3 3 44 4 19 2 Hisserich et aL H 340 R clereceive reflected signals and form respective Dop- 3,394,342 7/1968Walker 343/7 ED pler frequencies. A divider determines the relative ,3/1967 y t et all 3 PD angle between the vehicle and the object bycalculat- Thompson the ratio of these Doppler frequencies when the ratioexceeds a predetermined value, comparators diy ExaminerBenlamm Bol'cheltrect a signal to disable the AND circuit. Assistant Examiner-G. E.Montone Attorney-Toren and McGeady 28 Claims 9 Drawing Figures F m IVAVPMENIEBBEB n ma 3. 778.823 sum 1 a: a

FIG. IC

INVENTOR$ 1 U N E Hmoau IZAWA Trwmmofl ATTORN 5 PMENIEU MB 1 1 i9153778x323 SHEET 2 BF 4 FIG. 7

AINVENTORS HAzuo s TO TOHIO HISATSUNE BY HINORU IZAWA PATENIED on: 1 1ms SHKET 0? 4 INVENTOIS HAZUO SATO BY TQM/0 Hl-SATSUNE HINORUOLZMAiWA 0T an? zmmfi vEnicLE sAEETY DEVICE BACKGROUND OF THE INVENTION Thisinvention relates to vehicle safety devices, and particularly toapparatuses for preventing injury to passengcrs of a vehicle duringcollision.

When a moving vehicle such as an automobile collides with an object suchas another vehicle or an obstacle in its path, the occupants in thevehicle are thrown forward of their own inertia and strike hard againsta portion of the vehicle. The initial collision between the vehicle andthe object is called the primary crash. The occupants striking a portionof the interior of the vehicle is called the secondary crash. Suchsecondary crashes can seriously injure the occupants of the vehicle.

One system that attempts to prevent such injuries utilizes aconveniently located air bag capable of being inflated by delivering gasto the air bag upon occurrence of the primary collision between thevehicle and the object. Thus the vehicles occupants strike the air bagwhen they are thrown forward of their own inertia. The air bag isadapted to absorb the impact energy resulting from a collision bydeflation of the air bag. This protects the occupant or occupants frombeing injured in a secondary crash.

In order to actuate a safety device of the type described, a knownsystem utilizes an impact detector which physically detects as animpact, contact of the vehicle with an object. For example, one systemutilizes a contact needle protruding in the forward direction at thefront of the vehicle. It thus detects a crash when the contact needletouches any object.

Another system utilizes an accelerometer mounted in the vehicle. Acollision is thus detected when the accelerometer detects the suddendeceleration of the vehicle during the primary crash.

In such systems a protective apparatus such as an air bag is inflated bydelivering gas into the air bag only when an impact detector is actuatedby the impact force resulting from a collision. However, experimentsshow that the secondary crash usually follows the primary crash within avery short time interval, on the order of about 40 ms, after the instantat which the primary crash occurs. Therefore safety devices forprotecting vehicle passengers as described above cannot effect theirdesirable results unless inflation of the air bag is completed withinthe beforementioned short time interval prior to the occurrence of thesecondary crash.

In order to overcome this problem it has been proposed that the air bagbe inflated by utilizing gas produced in an explosion of black powder,or by utilizing gas supplied from a high pressure gas storage tank whichholds gas at pressures of the order of 200 to 300 atmospheres. However,such rapid inflation of an air bag may cause a sudden increase inpressure in the remaining portion of the interior of the vehicle,especially when it is completely or almost completely enclosed. This maysubject the occupants of the vehicle to secondary injuries, such asrupture of the tympanic membrane.

Moreover, in systems of the type which detect the vehicles impact force,the degree or probability of injuries which may be inflicted upon avehicles occupants may vary with the location of the impact detector orthe direction of the collision, even if the impact detector alwaysresponds to the same impact force. Additionally there may be a timedelay from the time of impact to the time the preset impact value isreached. This impact value is determined experimentally as the impactvalue at which injuries may be caused to a human body upon occurrence ofa secondary crash. This time delay is not uniform. Consequently, knownsystems utilizing the impact force have serious drawbacks that preventair bags from being fully effective.

An object of this invention is to eliminate the above mentioneddisadvantages.

Another object of the invention is to improve such safety devices.

Still another object of the invention is to assure cornplete inflationof an air bag before the secondary crash without inflating the bag sorapidly as to cause a sudden pressure increase in the interior space ofthe vehicle.

Yet another object of this invention is to protect the safety of avehicles occupants from injuries resulting from a secondary crash withsubstantial assurance and reliability and yet at the same time preventactuation of the safety device that protects the passengers, such as theinflation of an air bag, at times when actual crashes do not occur. Inother words, it is an object of this invention to actuate a safetydevice such as an inflatable air bag each time a crash occurs and toavoid such actuation at all other times.

SUMMARY OF THE INVENTION According to a feature of the invention atransmitting antenna and a receiving antenna, both having very sharpdirectivity, are mounted at the front of the vehicle carrying the'passengers to be protected and oriented so that the beams of the twoantennas intersect at a predetermined zone ahead of the vehicle.Generating means cause the transmitting antenna to radiate a signal andreceiving means coupled to the receiving antenna confirm the presence ofan object only when the object has entered the predetermined zone andreflected the radiated signals to the receiving antenna. The receivingmeans derive the speed of the object relative to the vehicle at the timethe object enters the predetermined zone. The zone is selected byorientation of the antennas so that only objects which would inevitablycrash into the vehicle enter the zone at speeds greater than a givenspeed. Thus the imminence of a primary crash is detected when an objectis detected and the relative speed exceeds the given speed or value.

By virtue of this feature the imminence of a primary crash is detectedwith certainty in advance of the primary crash. According to anotherfeature of the invention a collision detecting signal is produced whenthe object enters the predetermined zone at speeds greater than thegiven speeds so as to indicate an inevitable col lision. This collisiondetecting signal actuates a safety device such as an air bag forprotecting vehicle passengers when a potential collision of the vehiclewith an object in its path becomes definitely inevitable. This protectsthe safety ofthe vehicle's occupants from injuries resulting from asecondary crash.

Because of the last feature, inflation of the air bag can be startedbefore the primary collision and can be completed well before avehicle's occupant is thrown forward by his own inertia upon occurrenceof the primary crash.

These features thus provide a device for detecting potential collisions,wherein the inevitability of a primary crash is determined withcertainty and a collision detecting signal issues when the primary crashbecomes inevitable. This protects the vehicle's occupants from anysecondary crash.

According to still another feature of the invention, the generator meansgenerates undulatory signals of constant frequency, a microwave circuitin the receiving means derives a Doppler signal by mixing and detectingthe transmitted undulatory signal and the received undulatory signalreflected by the object, a frequency-voltage converter in the receivingmeans obtains a voltage proportional to the frequency of the Dopplersignal, a threshold circuit issues a signal'when the voltage exceeds apredetermined value, a speed threshold circuit issues a signal when thelevel of the Doppler signal exceeds a predetermined value, and anoperating AND circuit issues a collision detecting signal in response tothe output signals of both threshold circuits.

According to still another feature of the invention, transmitting andreceiving antennas are installed at the front left and front right sidesof the vehicle and the relative speeds between the vehicle and theobject are derived at the left and right sides from Doppler signalsobtained by left and right hand side microwave circuits. Calculatingmeans determine the relative angle between the vehicle and the object bymeans of a circuit capable of obtaining the ratio of the relative speedat the right and left sides. This detects the possibility of a collisionas compared to the object and the vehicle passing each other.

According to another feature of the invention, the collision detectingsignal is inhibited when an object in the path of the vehicle is amoving object such as an automobile and the angle made by the directionof movement of the object and that of the vehicle is great so that theywill not actually crash but pass each other. This also occurs when theobject passes directly in front of the vehicle. A collision detectingsignal is thus issued only when the relative angle is small and theoccurrence of a primary crash is inevitable.

These and other features of the invention are pointed out in the claims.Other objects and advantages of the invention will become obvious fromthe following detailed description when read in light of theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1A is a side elevation of anautomobile illustrating the intersecting directional beam patterns ofantennas mounted on the automobile;

FIG. 1B is a plan view of the automobile in FIG. 1A illustrating thebeam patterns formed by the intersections of a pair of antenna beams onthe right side of the automobile and a pair of antenna beams from theleft side of the automobile;

FIG. 1C is another plan view of the automobile in FIG. 1B illustratinganother antenna beam pattern comparable to that of FIG. 18;

FIG. 2 is an amplitude distance graph illustrating the amplitudes ofwave forms reflected from objects in the sensitive region;

FIG. 3 is a plan view of an automobile illustrating the angularrelationships between objects ahead of the vehicle and the antennas onthe vehicle so as to show the principle of the operation of anembodiment of this invention;

FIG. 4 is a block diagram illustrating the overall structure of anembodiment of the invention wherein the potential collision detectingsystem actuates a safety device employing an air bag for protecting thevehicle's passengers.

FIG. 5 is a perspective drawing illustrating the struc ture of microwavecircuits employed in an embodiment of this invention;

FIG. 6 is a detailed schematic circuit diagram of portions of thecircuit in FIG. 5; and

FIG. 7 is an operational characteristic diagram of the comparator usedin the circuit of an embodiment of this invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS In FIG. 1A a vehicle Mcarries a potential collision detecting device embodying features of theinvention. On the vehicle M a transmitting antenna A, radiatesmicrowaves along a radial beam S formed by the vertical directivity ofthe transmitting antenna. A receiving antenna A also mounted at thefront of the vehicle M forms a directive beam pattern G. Thetransmitting and receiving characteristics of the antennas arereverible. Therefore, if the two antennas have the same characteristicsthe beam S becomes identical to the beam G. The intersection of thebeams S and G, shown by the shaded portion in FIG. 1A form a sensitiveregion or zone Av. In FIG. 1A this sensitive region is illustrated inthe vertical direction when viewed laterally from the side of thevehicle M. Only when an object m enters this sensitive region Av are themicrowaves radiated from the transmitting antennas A, reflected from apoint P on the object m facing the vehicle M and received by thereceiving antenna A 57 According to the invention the antennas A, and Aof the potential collision detecting system are installed at angles sothat the region Av is located 1 to 2 meters ahead of the vehicle. Thestrength of the signal received rises when the vehicle M approaches theobject m that is to say the levels of the received undulatory signalsincrease as the distance D between the vehicle M and the object mdecreases. The variation of the levels of the received signal, by theantennas forming the sensitive region Av described above, is shown inFIG. 2.

In FIG. 2, the forward end of the vehicle M is indicated by 0, whichcoincides with the tips of the transmitting and receiving antennas A,and A In microwave circuits, an electromagnetic horn is frequently usedto improve the directivity. In such a case, this point coincides withthe open end of the horn. The abscissa represents the distance D betweenthe extreme end of a vehicle and an object. The ordinate represents thelevel H of the signal obtained by the receiving antenna A when thedistance between the vehicle and the object m is D. In other words, whenthe object m is located at a distance D or more from the vehicle, thelevel of the received signal is almost zero. This level increasessuddenly as the object m enters the sensitive region Av and furtherincreases as the object m approaches the vehicle M.

The distribution of the electromagnetic field of the microwaves is notuniform along the beam width. Rather it follows a normal distributionhaving a maximum value at the center axis of the beam. The level II ol'the received signal reaches a maximum at the position Dc where thecenter axes of the beams interscct. The level H of the received signaldecreases as the distance between the vehicle M and the object m furtherdecreases. Thus the relation of the distance D between the vehicle M andthe object m with respect to the level H is indicated by the envelope I.

As shown in FIG. 2, some degree of signal level is observed even whenthe distance between the vehicle and the object is less than D due tothe scatter of microwaves. However, for purposes of this invention evena high signal level at distances less than D produce no problems ortrouble.

The level of the received signal varies with the reflection factor anddimensions of the object m. Objects having high reflection factors orlarge reflection surfaces change the envelope to a form shown by thecurve f. However, here the sudden increase in level occurs at thedistance D This point never varies with the material, shape or othercharacteristics of the object. Therefore, the relative distance Dbetween the vehicle and the obstacle or object m can be accurately determined by this sensitive region or sensitivity zone Av which embodies afeature of this invention. More particularly the sensitive zone Avaccurately determines when an object is closer to the front of thevehicle than the end of the sensitive zone Av.

FIG. 1A illustrates the antennas A and A on one side of the vehicle M.These antennas A and A form an antenna pair A and are mounted on theright side of the vehicle as shown in FIG. 1A. According to theinvention a similar pair A of antennas is mounted on the left side ofthe vehicle. The two pairs of antennas are illustrated more particularlyin FIGS. 18 and 1C. FIGS. 18 and 1C also illustrate the sensitiveregions or zones Av of the antenna pair A and of the antenna pair A inthe horizontal direction when viewed from the top of the vehicle M. theleft hand antenna pair A forms the sensitive region which in thehorizontal direction has the shape indicated by the portion L This isdefined as the horizontal sensitive region or horizontal sensitive zone.The corresponding sensitive region formed by the right hand antenna pairA as viewed from the top is indicated by R The horizontal sensitiveregions L and R overlap in FIG. 1B. In FIG. 1C these sensitive regionsare formed so as to overlap with each other still more. This is done byspreading the horizontal directivities of the antenna pairs A and A Withthe antenna pairs A and A the presence of an object is detectedreliably, and with accuracy when the vehicle M approaches the object min its path closer than the predetermined distance D It is, of course,not necessary or desirable to utilize signals indicating the presence ofall objects within the sensitive region. For example, if the vehicle Mis parked behind another vehicle within the sensitive region it is notnecessarily desirable to utilize signals obtained from sensing the presence of the other vehicle. It is necessary to utilize the signals onlywhen there is a predetermined relative motion between the vehicles orbetween the vehicle M and the object m.

When the vehicle M approaches the object m at the relative speed v, thefrequency f, of the signal transmitted from the transmitting antenna A,is reflected from the object m and is received by the receiving antennaA At this time the frequency f, of the received signal is shifted due tothe Doppler effect. The Doppler frequcncy f thus obtained isapproximately expressed by the formula ln this formula c is thepropagation speed of microwaves.

As seen from the formula of l the Doppler frequency f is proportional tothe relative speed v. Therefore the relative speed v can be obtained bydetecting the Doppler frequency. If the distance between the vehicle Mand the object m is D and the distance and the object approaching eachother at a relative speed v the vehicle M will crash into the object mafter the time D/v. Under such conditions the collision is inevitablewithin the specified period of time because of the braking and steeringcharacteristics of the vehicle, however hard the brake is applied orhowever skillfully the vehicle is steered in an effort to avoid a crash.This specified period of time is determined experimentally. The systemaccording to this invention includes a controller mounted in the vehicleM and coupled to the antenna pairs A and A L to issue a collisiondetecting signal. This controller which includes the receiving meanscoupled to the receiving antennas A detects that the object M has comewithin the sensitive region A and the relative speed at this timeexceeds the predetermined value. The controller then actuates a devicesuch as an air bag or the like to protect the occupants of the vehicle.

The controller in the vehicle M also takes care of the situation whenthe object m enters the sensitive region at an angle which would avoid acrash so that the vehi' cle and the object pass each other withoutcrashing. That is to say the controller inhibits issuance of a collision detecting signal when the relative angle between the object m andthe vehicle M is sufficiently great so that even if the object m comeswithin the sensitive region the vehicle would not crash into the objectbut the two would pass each other. In order to determine whether thevehicle would actually crash into the object or whether they would passeach other the control ler determines the relative angle of travelbetween the two. The controller accomplishes the determination of therelative angle according to the principle described with reference toFIG. 3.

FIG. 3 illustrates the condition when the object m moves towards thevehicle M in the direction shown by the arrow at the speed v and therelative angle 6. The Doppler frequencies f obtained in the controllerfrom the left and right antenna pairs A and AR installed on the vehicleM under the above described condition are expressed as follows:

fdL 11/0) vcoset 2 fdn frl i: 3

In the above formulas f, and f are the Doppler frequencies derived bythe controller from signals detected by the left and right antenna pairsA and A respectively. 0,, and O are the angles formed by the respectiveantennas and the moving direction of the object m, respectively. Theratio off, and f is obtained as follows:

e f /f COSQL/COSGR 4 As shown in FIG. 3, the value c is equal to unitywhen the object m approaches the vehicle M from directly ahead. On theother hand the value of e is determined by calculation in the controllerwhen the object passes the vehicle without crashing into the vehicle. Inother words, the controller is set beforehand to issue collisiondetecting signals only within a predetermined range within which thevehicle and object will contact each other, depending upon the size ofthe vehicle, the position of the sensitive region and other factors.Thus the controller detects potential collisions and issues signalstherefore when the value of e is within the predetermined range. Thepredetermined range has its bounds when the object and the vehicle willjust contact each other.

FIGS. 4, and 6 illustrate details of the potential collision detectingdevice according to the invention including the controller. The entireapparatus is mounted within the vehicle M. In FIG. 4 a generator 1,namely the beforementioned generator, generates microwaves having apredetermined frequency. These signals from the generator are applied tothe antennas A that make up the transmitting antennas in the antennapairs A and A For simplicity, and especially to maintain continuity ofreference numerals in FIG. 4, the antennas A of the antenna pairs A andA are designated 2L and 2R. Thus the antenna 2L is the transmittingantenna which is installed at a desired location at the front left sideof the vehicle M and adapted to radiate microwaves. The antenna 2R isthe transmitting antenna which is installed at the desired location onthe front right side of the vehicle and adapted to radiate microwaves.The receiving antennas A in the antenna pairs A and A are designated 3Land 3R in FIG. 4. Thus the antenna 3L designates the receiving antennainstalled at the front of the vehicle M so that its beam intersects theradial beam of the transmitting antenna 2L at a predetermined position.Similarly the antenna 3R designates a receiving antenna which isinstalled at the front of the vehicle M so that its beam patternintersects the radial beam pattern of the transmitting antenna 2R at apredetermined position. The suffix L indicates those component partsmounted at or belonging to or concerned with the left side of thevehicle M. The suffix R in the reference characters indicate componentparts mounted on or belonging to or concerned with the right side of thevehicle M. Since these component parts perform the same function theexplanation will be limited to some extent to those mounted on the leftside. It will be understood therefore that the corresponding componentparts having the same numeral in the reference character but ending inthe suffix R cooperate with the other parts in the same manner asdescribed.

A directional coupler 4L couples the signals from the generator 1 to theantenna 2L. The coupler 4L further couples the reflected signals fromthe antenna 3L to a detector 5L together with part of the transmittedsignal originating in generator 1. The detector 5L applies a Dopplersignal composed of the difference frequency between the signal from thegenerator 1 and the signal in antenna 3L reflected from the object, toan amplifier 6L. A frequency-voltage converter 7L forms a voltage of theDoppler frequency and applies it to a threshold circuit 8L which issuesoutput signals only when the voltage exceeds a predetermined value. Athreshold circuit 9L also issues output signals only when the level ofthe output signal from the amplifying unit 6L exceeds a preset value.

The value of the constant voltage set at the threshold circuit 8L is avoltage corresponding to the critical relative speed at which therelative speed v is just low enough that no injury is inflicted on thevehicles occupants because of the very small impact force, even if thevehicle M crashes into the object m. The specified level set at thethreshold circuit 9L is the level H0. in FIG. 2. This level isdetermined as the critical level, which when exceeded, indicates thepresence of the object m in the sensitive region. The output voltage ofthe threshold circuit 9L is identified as the voltage V The outputvoltage of the threshold circuit SL is identified as V The existence ofvoltages V and V indicate that the left antennas 2L and 3L have detectedthe existence of an object m in their sensitive region and that theobject was traveling at a speed relative to the vehicle M greater thanthat predetermined to be harmful.

In the same manner as described above the generator 1 applies signals tothe antenna 2R and these signals are reflected in the sensitive zone orregion to the receiving antenna 3R. A directional coupler 4R applies acombination of the transmitted signal and received signal to a detector5R. An amplifier 6R, frequency to voltage converter 7R, thresholdcircuit 8R, and threshold circuit 9R operate identicaly with therespective components 5L, 6L, 7L, 8L and 9L to produce voltages V and VThe existence of the voltage V indicates the presence of an object inthe sensitive zone defined by the antenna 2R and SR. The existence of avoltage V indicates that the object in the sensitive region defined bythe antenna 2R and SR is traveling at a relative speed which isconsidered to be dangerous.

An OR gate circuit issues a signal when either of the threshold circuits9L or 9R issues their respective output signals V or V Thus, if thereexists an object in either of the sensitive regions defined by theantennas 2L and 3L or 2R and SR the OR gate circuit issues a signal V AnOR gate circuit issues a signal V when either of the threshold circuits8L or SR issues an output signal. Thus the voltage V appears if thespeed of the object in either of the sensitive regions relative to thevehicle M is determined to be dangerous.

A divider 12 calculates the ratio of the output voltages V and V of thefrequency voltage converters 7L and 7R. This divider in effect thenmeasures the ratio of the relative speed in the left sensitive zone ascompared to the relative speed in the right sensitive zone. A comparator13 issues an output signal only when the output 6 of the divider 12 iswithin the predetermined range. An AND gate circuit issues outputsignals only when the outputs are generated simultaneously from thecomparator 13, the OR gate circuit 10 and the OR gate circuit 11. Anamplifying unit 15 amplifies the output of the AND gate circuit 14.

A tank I6 storing high pressure gas for inflating an air bag 17installed in the vehicle M at the location where the secondary crash ismost likely to occur, communicates with the air bag when anelectromagnetic valve 18 between the tank and the air bag receives anoutput signal from the amplifying unit 15.

Further details of the operation of the potential collision detectingdevice described above are discussed hereinafter with reference to FIGS.5 and 6. These figures illustrate the device in more detail. In thesefigures parts corresponding to those of FIG. 4 are identified by thesame reference numeral.

The generator 1 comprises an oscillation circuit 21, a doubler circuit22, and a coaxial resonance circuit 23. The oscillation circuit 21includes an oscillating transistor 24, resonance capacitors 25 and 26, aresonance coil 27 and additional components utilized in standardoscillators. The initial frequency signal derived from the oscillatingcircuit 21 is directed to the idler circuit of a doubler circuit whichconsists of a plurality of coils and capacitors. Here a high harmonic isproduced by means of a varactor diode 28 provided at the output side ofthe idler circuit and having a non-linear characteristic. In the coaxialresonance circuit 23, the high harmonic of a specific order is taken outas microwaves by means of a resonant circuit including avariablecapacitor 29 and a coil 30.

As shown more particularly in FIG. the microwaves are directed through amain wave guide 41 to the two directional couplers 4L and 4R. Themicrowaves directed to the left hand directional coupler 4L radiatethrough the electromagnetic horn type transmitting an tenna 2L in theforward direction of the vehicle. An ob ject such as the object m in thesensitive region determined by the antenna 2L and 3L reflects themicrowaves. The latter are then received by the left hand side receivingantenna 3L. The signal thus received is again directed through anauxiliary wave guide 42 to the directional coupler 4L and is then passedto the detector 5L together with part of the transmitted signal.

The detector 5L includes a detecting diode 50. By utilizing thenon-linear characteristic of the diode, the Doppler signal having thedifference frequency between the output signal of the generator 1 andthe signal reflected from the object is obtained. The Doppler signal isamplified by the linear amplifying unit 6L. The latter comprises anamplifier 61, and input resistor 62, a negative feedback resistor 63 anda gain adjusting resistor 64. The output of the linear amplifier is fedinto the frequency voltage converter 7L and the threshold circuit 9L.

The frequency voltage converter 7L includes a saturation amplifyingcircuit having an amplifier 70, an input resistor 72 and a negativefeedback resistor 73. It also includes a frequency voltage convertingcircuit 71. This circuit produces a unidirectional voltage, that is adirect-current voltage, V proportional to the frequency of the Dopplersignal. A threshold circuit 8L receives the output voltage V andproduces a signal voltage V only when the unidirectional voltage Vexceeds a specified value. In the threshold circuit 8L an amplifier 84and resistors 85, 88 and 89 form an amplifying circuit which furtherincludes a bias circuit composed of resistor 86 and 87. The thresholdvoltage is set by adjusting the resistor 87 with respect to the voltageto be applied to the bias circuit.

The Doppler signal applied to the threshold circuit 9L is rectified by avoltage doubler diode circuit comprising capacitors 91 and 94 and diodes92 and 93. The Doppler signal is converted to a unidirectional voltageproportional to the level of the Doppler signal. Then, this voltage isapplied to a non-sensitive circuit comprising a linear amplifier circuitwith an amplifier 98 and resistors 95, 99, 100 and a bias circuit ofresistors 96 and 97. The signal V is derived from the threshold circuit91. only when the direct current voltage, that is the unidirectionalvoltage, exceeds a certain value.

The microwave components identified as 1, 2R, 3R, 4R, and SR, and thecircuits 6R, 7R, SR and 9R on the right side of the vehicle M serve toprocess the Doppler signal in a manner substantially identical to thesecomponents and circuits having the same numeral but with the suffix L.The voltage V is derived from the frequency voltage converter 7R. Thesignal V and V are derived from the threshold circuits SR and 9R,respectively. The voltage V,, and V are applied to the divider 12 whichderives the voltage V. proportional to the ratio 5 =VL/V of the twovoltages V and V The voltage Va is applied to the comparator 13 and asignal V is issued only when the value V is within a predeterminedrange. The output signals V and V. from the threshold circuit 8L and SRare directed to the OR gate circuit 11. The output signal V issues fromthe OR gate circuit 11 when at least either of the output signals ispresent. The output signals V and V from the threshold circuit 9L and 9Rappear at the OR gate circuit 10. The output signal V issues from the ORgate circuit 10 when at least either of these output signals is present.The signals V,, V and V are directed to the AND gate circuit 14. Thelatter issues a signal V. only when all of these signals applied theretoare present. The signal V then appears at the amplifying unit 15.

As illustrated in FIG. 1A the transmitting antenna is installed belowthe receiving antenna. This method. of installation of antennas iseffective to reduce noise resulting from irregular reflection ofradiation from the road surface, from scatter, or the like. Thethreshold voltages set at the threshold circuit 9L and 9R correspond tothe level H0 illustrated in FIG. 2. They furnish the limit forconfirming that the object m has entered the sensitive region. Thethreshold voltages set at the threshold circuit 8L and 8R correspond tothe limit of the relative speed where the relative speed is low enoughso that secondary crash inflicting injury on a vehicle occupant does notoccur even if the primary crash occurs. That is to say it is set toproduce a signal only when a dangerous crash would occur.

The voltage setting range of the comparator 13 depends on the limit ofwhat would be a mere contact which is indicated by the relative angle 6.This range is determined so that the output signal V issues when 6 comeswithin the range between 5 and 6 obtained from calculation andillustrated in FIG. 7.

The presence of the object m in the sensitive region defined by theantennas is indicated by issuance of signals from either of thethreshold circuits 9L or 9R. The magnitude of the relative speed v canbe determined by the output signal from either of the threshold circuits8L or 8R. Thus, the inevitability of a primary crash can be detected bythe existance of an output signal from the comparator 13. The outputsignal V, of the AND gate circuit 14 represents a collision detectingsignal.

The apparatus described above detects the imminence of a potentialcollision, with certainty, prior to occurrence of the primary crash.Thus, it makes possible the inflation of an air bag capable of absorbingthe impact energy from a secondary crash well in advance of theoccurrence of the secondary crash and with thorough certainty andreliability. Formation of the sensitive region in measuring the relativedistance between the vehicle and the object completely eliminatesshortcomings such as the variation of reflected factor due to thematerial of the object m, the shape and other chracteristics of theobject, the variation of the energy of the reflected signal due to thesize of the object, and the variation due to weather conditions such asrain, snow,

'or the like. This greatly raises the accuracy of detection of apotential collision. Additionally the provision of the object detectingmeans at both sides of the vehicle M makes it possible to detect withcertainty whether a vehicle is on a collision course with an object orwhether they will pass each other. Therefore, there is virtually nopossibility of erroneous actuation of the safety device even in citiesand towns where traffic volume is quite high.

If the sensitive region or zone is appropriately set, the detection of apotential collision can be accurately accomplished without detecting therelative angle. In such a case it is not necessary to provide two setsof transmitting and receiving antennas at both sides of a vehicle. i

In the above described embodiment, one pair of transmitting andreceiving antennas is provided on the left side of the vehicle and onepair on the right side of the vehicle. According to another embodimentof the invention one transmitting antenna is located in the center ofthe vehicle and two receiving antennas are located at the left and rightsides.

According to one embodiment of the invention, the directional couplers4R and 4L are employed as a means for carrying out homodyne detection.When the received signal is to be obtained by homodyne detection, it isobtained by comparing the phase of the transmitted signal and that ofthe reflected signal. Therefore, if the object m within the sensitiveregion gets closer to the vehicle by one half wavelength of themicrowave signal, the path of undulatory signal is decreased by one fullwavelength. Thus the phase is advanced 360. In other words, the phasesof the transmitted and received signals are advanced 360 each time therelative distance between the vehicle and the object is changed by ahalf wavelength. When the phases are synchronized during the aboveperiod the phases overlap, producing peaks. If the phases deviate by180", an anti-phase results. This produces dips. Thus the frequency f,of the signal to be obtained by homodyne detection as the vehicleapproaches the object is expressed by the formula:

here A is the wavelength of the microwave signal. Since the wavelength Acan be expressed as c/fl, the formula (5) can be rewritten as follows:

This can be interpreted to means that the frequency f of the undulatorysignal obtained by homodyne detection is equal to the Doppler frequencyf,,. In other words, detection of a potential collision can be done inthe same manner as described herein before by measuring the frequency ofthe signal obtained by homodyne detection.

According to another embodment of the invention homodyne detection isaccomplished by employing a combination of conventinal 3-portcirculators instead of the directional couplers 4L and 4R. In eithercase, as described above, embodiments according to the invention detecta potential collision accurately and with certainty in advance of suchcollision by utilizing the undulatory signals to provide a sensitiveregion, or a sensitivity zone, in measuring the relative speed.

While embodiments of the invention have been described in detail it willbe obvious to those skilled in the art that the invention may beembodied otherwise without departing from its spirit and scope.

What is claimed is:

1. A system for responding to potential collisions of a conveyance andan object, comprising transmitting means mounted on said conveyance fortransmitting undulatory radiation along a pattern having defined bounds,receiving means mounted on said conveyance for receiving reflectedundulatory radiation along a second radiation pattern having definedbounds, said transmitting means and said receiving means beingvertically displaced relative to each other, said patterns havingvertical and horizontal bounds, said transmission and receiving meansforming the pattenrs so as to cause the second pattern to intersect thefirst radiation pattern at a sufficient vertical angle so as to definewith the vertical bounds of the first pattern at the intersection of thepatterns a sensitivity region having horizontally defined bounds atleast at the portion of the region more remote from the conveyance thanthe remainder of the region, detecting means responsive to saidreceiving means and transmitting means for responding to the frequencyreceived by said receiving means different from the first frequency andfor producing an indication when the difference exceeds a predetermineddifference.

2. A system as in claim 1, wherein said transmitting means includesantenna means on the conveyance and coupled to said detecting means fortransmitting the undulatory radiation along the first pattern, andwherein said receiving means includes receiving antenna means mounted onsaid conveyance and coupled to said detecting means for receiving theundulatory radiation along the second pattern, said antenna means eachdirecting their pattern ahead of the vehicle so the patterns intersectat an acute angle.

3. A system as in claim 1, wherein said detecting means includes Dopplersensing means for producing a Doppler signal which is a measure of thespeed of an object in the sensitivity zone, said horizontal patternsbeing sufficiently wide so that the sensitivity zone extends across thewidth of the conveyance.

4. A system as in claim 3, wherein said detecting means includesfrequency to voltage converter means coupled to said Doppler means forproducing a voltage proportional to the frequency of the Doppler signal,said detecting means further including threshold means connected to saidconverter means for inhibiting the output signal unless it exceeds agiven value.

5. A system as in claim 4, wherein said detecting means further includessecond threshold means connected to said Doppler sensing means forproducing a control signal only when the level of the Doppler signalexceeds a predetermined value, and AND means for producing signals onlyin response to signals from both of said threshold means.

6. A system as in claim 1 wherein the pattern defined by said receivingmeans includes a plurality of beams each intersecting the transmittedpattern, and wherein said detecting means detects the difference betweenthe frequency of said pattern and the frequency of reflected signalsreceived along each of the beams, and

output means in said detecting means for producing an output only whenthe differences between each of the reflected signals received by saidreceiving means and the first frequency exceeds a predetermineddifference, said horizontal patterns being sufficiently wide so that thesensitivity zone extends across the width of the conveyance.

7. A system as in claim 6, wherein said detecting means includes Dopplersensing means for each of the beams and the pattern.

8. A system as in claim 7, wherein said detecting means includes aplurality of frequency to voltage converter means each coupled to one ofsaid detecting means for producing a voltage proportional to the fre- Vquency of the Doppler signal, said detecting means further including aplurality of threshold means each connected to said converter means forinhibiting output of signals from said converter means unless the signalexceeds a given value.

9. A system as in claim 8, wherein said detecting means includes aplurality of second threshold means each connected to said Dopplersensing means for producing a signal from each only when the level ofthe corresponding Doppler signal exceeds a predetermined value, and ANDmeans connected to each of said first and second threshold means forproducing signals only when both of said first and second thresholdmeans produce signals.

10. A system as in claim 6, wherein said detecting means includesdivider means for comparing the frequency differences established insaid detecting means for each of the beams and the pattern, andcomparator means for inhibiting the output signal unless the comparisonlies within a predetermined range.

11. A system as in claim 9, wherein said detecting means includesdividing means connected to each of said frequency to voltage convertermeans for establishing a relationship between the frequency differencesdetected by said Doppler means, and comparator means for producing asignal and applying it to said AND means only when the relationship lieswith a given range.

12. A system as in claim 6, wherein said transmitting means includes aplurality of transmitting antennas and said receiving means includes aplurality of receiving antennas vertically displaced from respectiveones of said transmitting antennas, each transmitting antennatransmitting undulatory radiation along the beam and each receivingantenna defining a beam vertically intersecting at least one of thebeams transmitted by said transmitting antenna.

113. A system as in claim 10, wherein said transmitting means includes aplurality of transmitting antennas and said receiving means includes aplurality of receiving antennas vertically displaced from respectiveones of said transmitting antennas, each transmitting antennatransmitting undulatory radiation along a beam, each receiving antennadefining a beam vertically intersecting at least a respective one of thebeams transmitted by said transmitting antennas.

14. A system as in claim 11, wherein said transmitting means includes apair of transmitting antennas and said receiving means includes a pairof receiving antennas vertically displaced from respective ones of saidtransmitting antennas, each transmitting antenna transmitting undulatoryradiation along a beam, and each receiving antenna defining a beamvertically intersecting a respective one of the beams transmitted bysaid transmitting antennas, said pair of transmitting antennas beinglocated on opposite sides of the front of the conveyance, said pair ofreceiving antennas being located on opposite sides of the front of theconveyance.

15. A system as in claim 6, wherein said transmitting means includes atransmitting antenna mounted on the vehicle and said receiving meansincludes four receiving antennas mounted around said transmittingantenna.

16. A potential collision detecting device, comprising a generator whichgenerates an undulatory signal having a first frequency, a transmittingantenna which radiates said undulatory signal, a receiving antennahaving a receiving axis intersecting the radiation axis of thetransmitting antenna within a predetermined region and adapted toreceive the undulatory signal from a reflected object and having asecond frequency, said receiving and transmitting antennas radiating andreceiving the undulatory signals along respective beams which aresufficiently narrow and intersect each other at a sufficient angle sothat the beams converge and then overlap and then completely divergefrom each other, sensing means for obtaining a Doppler signal having afrequency difference between the two frequencies, a frequency voltageconverter for obtaining an electrical quantity proportional to thefrequency of the Doppler signal, a first circuit which issues signalsonly when the electrical quantity exceeds a predetermined value, asecond circuit which issues a signal only when the level of the Dopplersignal exceeds a predetermined value, and an AND circuit for issuing asignal only when both the first and second circuits issue signals, saidtransmitting antenna and said receiving an tenna being verticallydisplaced relative to each other and producing the beams so that theyspread horizontally and so that the beams converge vertically and thenoverlap vertically and then completely diverge from each othervertically.

17. A potential collision detecting device, comprising a generator forgenerating an undulatory signal having a first frequency, a firsttransmitting antenna for radiating said undulatory signal, a firstreceiving antenna having a receiving axis intersecting the radiationaxis of the first transmitting antenna within a predetermined region andadapted to receive reflected signals having a second frequency, saidfirst transmitting and receiving antennas being vertically displacedrelative to each other, said first transmitting antenna and said firstreceiving antenna respectively radiating and receiving the undulatorysignals along beams sufficiently narrow in the vertical direction and ata sufficient angle in the vertical direction so that the beams as awhole converge in the vertical direction and then overlap in thevertical direction and then diverge in the vertical direction so that noportion of the beams continue to overlap in the vertical direction,sensing means connected to each of said antennas for obtaining a firstDoppler sig nal having the difference frequency between said twofrequencies, a second transmitting antenna which radiates undulatorysignals having the first frequency, a second receiving antenna having areceiving axis intersecting the radiation axis of said secondtransmitting antenna within a predetermined region and adapted toreceive reflected undulatory signals having a third frequency, saidsecond transmitting and receiving antennas being vertically displacedrelative to each other, said second transmitting antenna and said secondreceiving antenna respectively radiating and receiving undulatorysignals along beams which are sufficiently narrow in the verticaldirection and intersect at a sufficient angle in the vertical directionso that the beams first converge in the vertical direction and thenoverlap in the vertical direction and then diverge in the verticaldirection without an overlap in the vertical direction, second sensingmeans for obtaining a second Doppler signal having the differencefrequency between said first and third frequencies, circuit means forobtaining a first electrical quantity proportional to the frequency ofthe first Doppler signal, second circuit means for obtaining a secondelectrical quantity proportional to the frequency of the second Dopplersignal, said first and second circuit means each being connected torespective ones of said sensing means, a divider connected to said firstand second circuit means for obtaining an electrical quantityproportional to the ratio of the first electrical quantity and thesecond electrical quantity, first comparator means connected to saiddivider for issuing signals only when the output of said divider iswithin a predetermined range, second comparator means connected to saidfirst circuit means for issuing signals only when the first electricalquantity exceeds a predetermined value, third comparator means connectedto said second circuit means for issuing signals only when the secondelectrical quantity exceeds a predetermined value, a first OR circuitconnected to the outputs of said second and third comparator means forcalculating the existence of outputs at either of said comparator means,a fourth comparator means connected to said first sensing means forderiving as output when the level of said first Doppler signal exceeds apredetermined value, fifth comparator means connected to said secondsensing means for deriving an output when the level of the secondDoppler signal exceeds a predetermined value, a second OR circuitconnected to said fourth and fifth comparator means for passing thesignals from either of said fourth or fifth comparator means, and an ANDcircuit connected to said first comparator means, said first OR circuitand said second OR circuit for issuing signals when output signalssimultaneously appear at said first comparator means, said first ORcircuit and said second OR circuit, said antennas radiating andreceiving beams wider in the vertical direction than the horizontaldirection so as to cause the overlaps formed by the beams to extendacross the width of the conveyance but remain within the width of theconveyance.

18. A system as in claim 1, further comprising output means forproducing an actuating signal, barrier means for producing a safetybarrier at locations in the conveyance where passengers are expected tostrike the conveyance in the event of a collision, said barrier meansbeing actuated by said output means.

19. A system as in claim 1, wherein said transmitting means and saidreceiving means define the patterns at such an angle that thesensitivity region formed thereby is completely bounded.

20. A vehicle for carrying passengers, comprising structure means havinga front and a rear end, electrically actuable safety means mounted onthe structure for selectively inserting a barrier between passengers andthe structure in the event of a collision of the vehicle, transmittingmeans mounted on the front of said structure for transmitting undulatoryradiation along a pattern having defined bounds, receiving means mountedon the front of said structure for receiving reflected and undulatoryradiation along a second radiation pattern having defined bounds andintersecting the first pattern at a sufficient angle so as to definewith the bounds of the patterns at the intersection of the patterns asensitivity region, said transmitting means and said receiving meanstransmitting and receiving the undulatory radiation along the patternsso that the patterns first converge and then overlap and then stopoverlapping and diverge without overlap, detecting means responsive tosaid receiving means and said transmitting means for responding tofrequencies received by said receiving means different from thefrequency by said transmitting means and producing a signal when thedifference exceeds a predetermined difference, output means connected tosaid detecting means and responsive to the thus produced signal andconnected to said safety means for producing an actuating signalactuating said safety means, said transmitting means having atransmitting antenna transmitting the undulatory radiation along thepattern, said receiving means having a receiving antenna verticallyaligned with the transmitting antenna and receiving the reflectedundulatory radiation along the second radiatisn pattern, the secondradiation pattern intersecting the first radiation pattern at a verticalangle, the antennas transmitting and receiving the undulatory radiationalong the patterns so that the patterns first converge vertically andthen overlap vertically and then stop overlapping vertically and divergewithout overlap vertically, said antennas producing bounds so theoverlap is wider horizontally than vertically.

21. A system as in claim 1, wherein the patterns first convergevertically, then overlap vertically and then stop overlapping verticallyand diverge vertically. 3

22. A system as in claim 1, wherein said transmitting means includingfirst and second transmitting antennas, said receiving means including afirst receiving antenna vertically aligned with said first transmittingantenna and a second receiving antenna vertically aligned with saidsecond transmitting antenna, said patterns from said transmitting meanseach having two portions each portion defined by one of saidtransmitting antennas, said patterns of said receiving means having twoportions each portion being formed by one of said receiving antennas,said transmitting means and said receiving means forming two overlapportions, said first transmitting and receiving antennas forming thefirst overlap portion and said second transmitting and receivingantennas forming the second overlap portion, said overlap portionextending only along the dimension of the conveyance transverse to thedirection of the patterns from the antennas, the patterns extending fromthe antennas substantially in the direction forward of the conveyance.

23. A system as in claim 1, wherein the region extends only up to afinite distance from the conveyance and back toward the conveyance.

24. An apparatus as in claim 23, wherein objects within the regioncloser to the conveyance than said distance reflect radiation from saidtransmitting means to said receiving means, and objects outside of there gion and beyond said distance fail to reflect radiation from saidtransmitting means to said receiving means.

25. A system as in claim 24, wherein said distance is less than severalcar lengths.

28. A system as in claim 16, wherein said beams stop overlapping andbegin to diverge less than one conveyance length from the conveyance.

1. A system for responding to potential collisions of a conveyance andan object, comprising transmitting means mounted on said conveyance fortransmitting undulatory radiation along a pattern having defined bounds,receiving means mounted on said conveyance for receiving reflectedundulatory radiation along a second radiation pattern having definedbounds, said transmitting means and said receiving means beingvertically displaced relative to each other, said patterns havingvertical and horizontal bounds, said transmission and receiving meansforming the pattenrs so as to cause the second pattern to intersect thefirst radiation pattern at a sufficient vertical angle so as to definewith the vertical bounds of the first pattern at the intersection of thepatterns a sensitivity region having horizontally defined bounds atleast at the portion of the region more remote from the conveyance thanthe remainder of the region, detecting means responsive to saidreceiving means and transmitting means for responding to the frequencyreceived by said receiving means different from the first frequency andfor producing an indication when the difference exceeds a predetermineddifference.
 2. A system as in claim 1, wherein said transmitting meansincludes antenna means on the conveyance and coupled to said detectingmeans for transmitting the undulatory radiation along the first pattern,and wherein said receiving means includes receiving antenna meansmounted on said conveyance and coupled to said detecting means forreceiving the undulatory radiation along the second pattern, saidantenna means each directing their pattern ahead of the vehicle so thepatterns intersect at an acute angle.
 3. A system as in claim 1, whereinsaid detecting means includes Doppler sensing means for producing aDoppler signal which is a measure of the speed of an object in thesensitivity zone, said horizontal pattErns being sufficiently wide sothat the sensitivity zone extends across the width of the conveyance. 4.A system as in claim 3, wherein said detecting means includes frequencyto voltage converter means coupled to said Doppler means for producing avoltage proportional to the frequency of the Doppler signal, saiddetecting means further including threshold means connected to saidconverter means for inhibiting the output signal unless it exceeds agiven value.
 5. A system as in claim 4, wherein said detecting meansfurther includes second threshold means connected to said Dopplersensing means for producing a control signal only when the level of theDoppler signal exceeds a predetermined value, and AND means forproducing signals only in response to signals from both of saidthreshold means.
 6. A system as in claim 1 wherein the pattern definedby said receiving means includes a plurality of beams each intersectingthe transmitted pattern, and wherein said detecting means detects thedifference between the frequency of said pattern and the frequency ofreflected signals received along each of the beams, and output means insaid detecting means for producing an output only when the differencesbetween each of the reflected signals received by said receiving meansand the first frequency exceeds a predetermined difference, saidhorizontal patterns being sufficiently wide so that the sensitivity zoneextends across the width of the conveyance.
 7. A system as in claim 6,wherein said detecting means includes Doppler sensing means for each ofthe beams and the pattern.
 8. A system as in claim 7, wherein saiddetecting means includes a plurality of frequency to voltage convertermeans each coupled to one of said detecting means for producing avoltage proportional to the frequency of the Doppler signal, saiddetecting means further including a plurality of threshold means eachconnected to said converter means for inhibiting output of signals fromsaid converter means unless the signal exceeds a given value.
 9. Asystem as in claim 8, wherein said detecting means includes a pluralityof second threshold means each connected to said Doppler sensing meansfor producing a signal from each only when the level of thecorresponding Doppler signal exceeds a predetermined value, and ANDmeans connected to each of said first and second threshold means forproducing signals only when both of said first and second thresholdmeans produce signals.
 10. A system as in claim 6, wherein saiddetecting means includes divider means for comparing the frequencydifferences established in said detecting means for each of the beamsand the pattern, and comparator means for inhibiting the output signalunless the comparison lies within a predetermined range.
 11. A system asin claim 9, wherein said detecting means includes dividing meansconnected to each of said frequency to voltage converter means forestablishing a relationship between the frequency differences detectedby said Doppler means, and comparator means for producing a signal andapplying it to said AND means only when the relationship lies with agiven range.
 12. A system as in claim 6, wherein said transmitting meansincludes a plurality of transmitting antennas and said receiving meansincludes a plurality of receiving antennas vertically displaced fromrespective ones of said transmitting antennas, each transmitting antennatransmitting undulatory radiation along the beam and each receivingantenna defining a beam vertically intersecting at least one of thebeams transmitted by said transmitting antenna.
 13. A system as in claim10, wherein said transmitting means includes a plurality of transmittingantennas and said receiving means includes a plurality of receivingantennas vertically displaced from respective ones of said transmittingantennas, each transmitting antenna transmitting undulatory radiationalong a beam, each receiving antenna defining a beam verticallyinterSecting at least a respective one of the beams transmitted by saidtransmitting antennas.
 14. A system as in claim 11, wherein saidtransmitting means includes a pair of transmitting antennas and saidreceiving means includes a pair of receiving antennas verticallydisplaced from respective ones of said transmitting antennas, eachtransmitting antenna transmitting undulatory radiation along a beam, andeach receiving antenna defining a beam vertically intersecting arespective one of the beams transmitted by said transmitting antennas,said pair of transmitting antennas being located on opposite sides ofthe front of the conveyance, said pair of receiving antennas beinglocated on opposite sides of the front of the conveyance.
 15. A systemas in claim 6, wherein said transmitting means includes a transmittingantenna mounted on the vehicle and said receiving means includes fourreceiving antennas mounted around said transmitting antenna.
 16. Apotential collision detecting device, comprising a generator whichgenerates an undulatory signal having a first frequency, a transmittingantenna which radiates said undulatory signal, a receiving antennahaving a receiving axis intersecting the radiation axis of thetransmitting antenna within a predetermined region and adapted toreceive the undulatory signal from a reflected object and having asecond frequency, said receiving and transmitting antennas radiating andreceiving the undulatory signals along respective beams which aresufficiently narrow and intersect each other at a sufficient angle sothat the beams converge and then overlap and then completely divergefrom each other, sensing means for obtaining a Doppler signal having afrequency difference between the two frequencies, a frequency voltageconverter for obtaining an electrical quantity proportional to thefrequency of the Doppler signal, a first circuit which issues signalsonly when the electrical quantity exceeds a predetermined value, asecond circuit which issues a signal only when the level of the Dopplersignal exceeds a predetermined value, and an AND circuit for issuing asignal only when both the first and second circuits issue signals, saidtransmitting antenna and said receiving antenna being verticallydisplaced relative to each other and producing the beams so that theyspread horizontally and so that the beams converge vertically and thenoverlap vertically and then completely diverge from each othervertically.
 17. A potential collision detecting device, comprising agenerator for generating an undulatory signal having a first frequency,a first transmitting antenna for radiating said undulatory signal, afirst receiving antenna having a receiving axis intersecting theradiation axis of the first transmitting antenna within a predeterminedregion and adapted to receive reflected signals having a secondfrequency, said first transmitting and receiving antennas beingvertically displaced relative to each other, said first transmittingantenna and said first receiving antenna respectively radiating andreceiving the undulatory signals along beams sufficiently narrow in thevertical direction and at a sufficient angle in the vertical directionso that the beams as a whole converge in the vertical direction and thenoverlap in the vertical direction and then diverge in the verticaldirection so that no portion of the beams continue to overlap in thevertical direction, sensing means connected to each of said antennas forobtaining a first Doppler signal having the difference frequency betweensaid two frequencies, a second transmitting antenna which radiatesundulatory signals having the first frequency, a second receivingantenna having a receiving axis intersecting the radiation axis of saidsecond transmitting antenna within a predetermined region and adapted toreceive reflected undulatory signals having a third frequency, saidsecond transmitting and receiving antennas being vertically displacedrelative to each other, said seconD transmitting antenna and said secondreceiving antenna respectively radiating and receiving undulatorysignals along beams which are sufficiently narrow in the verticaldirection and intersect at a sufficient angle in the vertical directionso that the beams first converge in the vertical direction and thenoverlap in the vertical direction and then diverge in the verticaldirection without an overlap in the vertical direction, second sensingmeans for obtaining a second Doppler signal having the differencefrequency between said first and third frequencies, circuit means forobtaining a first electrical quantity proportional to the frequency ofthe first Doppler signal, second circuit means for obtaining a secondelectrical quantity proportional to the frequency of the second Dopplersignal, said first and second circuit means each being connected torespective ones of said sensing means, a divider connected to said firstand second circuit means for obtaining an electrical quantityproportional to the ratio of the first electrical quantity and thesecond electrical quantity, first comparator means connected to saiddivider for issuing signals only when the output of said divider iswithin a predetermined range, second comparator means connected to saidfirst circuit means for issuing signals only when the first electricalquantity exceeds a predetermined value, third comparator means connectedto said second circuit means for issuing signals only when the secondelectrical quantity exceeds a predetermined value, a first OR circuitconnected to the outputs of said second and third comparator means forcalculating the existence of outputs at either of said comparator means,a fourth comparator means connected to said first sensing means forderiving as output when the level of said first Doppler signal exceeds apredetermined value, fifth comparator means connected to said secondsensing means for deriving an output when the level of the secondDoppler signal exceeds a predetermined value, a second OR circuitconnected to said fourth and fifth comparator means for passing thesignals from either of said fourth or fifth comparator means, and an ANDcircuit connected to said first comparator means, said first OR circuitand said second OR circuit for issuing signals when output signalssimultaneously appear at said first comparator means, said first ORcircuit and said second OR circuit, said antennas radiating andreceiving beams wider in the vertical direction than the horizontaldirection so as to cause the overlaps formed by the beams to extendacross the width of the conveyance but remain within the width of theconveyance.
 18. A system as in claim 1, further comprising output meansfor producing an actuating signal, barrier means for producing a safetybarrier at locations in the conveyance where passengers are expected tostrike the conveyance in the event of a collision, said barrier meansbeing actuated by said output means.
 19. A system as in claim 1, whereinsaid transmitting means and said receiving means define the patterns atsuch an angle that the sensitivity region formed thereby is completelybounded.
 20. A vehicle for carrying passengers, comprising structuremeans having a front and a rear end, electrically actuable safety meansmounted on the structure for selectively inserting a barrier betweenpassengers and the structure in the event of a collision of the vehicle,transmitting means mounted on the front of said structure fortransmitting undulatory radiation along a pattern having defined bounds,receiving means mounted on the front of said structure for receivingreflected and undulatory radiation along a second radiation patternhaving defined bounds and intersecting the first pattern at a sufficientangle so as to define with the bounds of the patterns at theintersection of the patterns a sensitivity region, said transmittingmeans and said receiving means transmitting and receiving the undulatoryradiation Along the patterns so that the patterns first converge andthen overlap and then stop overlapping and diverge without overlap,detecting means responsive to said receiving means and said transmittingmeans for responding to frequencies received by said receiving meansdifferent from the frequency by said transmitting means and producing asignal when the difference exceeds a predetermined difference, outputmeans connected to said detecting means and responsive to the thusproduced signal and connected to said safety means for producing anactuating signal actuating said safety means, said transmitting meanshaving a transmitting antenna transmitting the undulatory radiationalong the pattern, said receiving means having a receiving antennavertically aligned with the transmitting antenna and receiving thereflected undulatory radiation along the second radiatisn pattern, thesecond radiation pattern intersecting the first radiation pattern at avertical angle, the antennas transmitting and receiving the undulatoryradiation along the patterns so that the patterns first convergevertically and then overlap vertically and then stop overlappingvertically and diverge without overlap vertically, said antennasproducing bounds so the overlap is wider horizontally than vertically.21. A system as in claim 1, wherein the patterns first convergevertically, then overlap vertically and then stop overlapping verticallyand diverge vertically. 3
 22. A system as in claim 1, wherein saidtransmitting means including first and second transmitting antennas,said receiving means including a first receiving antenna verticallyaligned with said first transmitting antenna and a second receivingantenna vertically aligned with said second transmitting antenna, saidpatterns from said transmitting means each having two portions eachportion defined by one of said transmitting antennas, said patterns ofsaid receiving means having two portions each portion being formed byone of said receiving antennas, said transmitting means and saidreceiving means forming two overlap portions, said first transmittingand receiving antennas forming the first overlap portion and said secondtransmitting and receiving antennas forming the second overlap portion,said overlap portion extending only along the dimension of theconveyance transverse to the direction of the patterns from theantennas, the patterns extending from the antennas substantially in thedirection forward of the conveyance.
 23. A system as in claim 1, whereinthe region extends only up to a finite distance from the conveyance andback toward the conveyance.
 24. An apparatus as in claim 23, whereinobjects within the region closer to the conveyance than said distancereflect radiation from said transmitting means to said receiving means,and objects outside of the region and beyond said distance fail toreflect radiation from said transmitting means to said receiving means.25. A system as in claim 24, wherein said distance is less than severalcar lengths.
 26. A system as in claim 24, wherein said distance is lessthan one car length.
 27. A system as in claim 1, wherein the portion ofthe region more remote from the conveyance than the remainder of theregion is less than one car length.
 28. A system as in claim 16, whereinsaid beams stop overlapping and begin to diverge less than oneconveyance length from the conveyance.